The invention is in the field of electronic reproduction technology and is directed to a method for engraving printing cylinders for rotogravure, whereby at least two engraving lanes of predetermined lane widths lying next to one another in axial direction are engraved with a respectively allocated engraving element, and is also directed to an electronic engraving machine for the implementation of the method.
When engraving printing cylinders in an electronic engraving machine, the engraving element that, for example, comprises an engraving stylus as a cutting tool, moves axially along a rotating printing cylinder continuously or in steps. The engraving stylus controlled by an engraving control signal cuts a sequence of depressions, referred to below as cups, arranged in an engraving raster into the generated surface of the printing cylinder. The engraving control signal is formed from the superimposition of an engraving signal representing the tonal values between "black" and "white" with a periodic raster signal. Whereas the periodic raster signal effects a vibrating lifting motion of the engraving stylus, the engraving signal controls the depths of the cups engraved into the generated surface of the printing cylinder in conformity with the tonal values to be reproduced.
For magazine printing, a plurality of strip-shaped cylinder regions, called engraving lanes, that lie axially next to one another must be simultaneously engraved with a respective engraving element on a printing cylinder or, respectively, on the printing cylinders of a color set that are successively engraved in one engraving machine or, on the other hand, are engraved simultaneously in a plurality of engraving machines. For example, the various printed pages of a print job are engraved in the individual engraving lanes. The engraving elements allocated to the individual engraving lanes are mounted on a common engraving carriage that moves along the printing cylinder in an axial direction during engraving.
A prerequisite for a good reproduction quality is the registration-exact adherence to the lane widths of the individual engraving lanes in the axial direction of the printing cylinder. In order to achieve a registration-exact engraving of the engraving lanes, the distances between the engraving stylus tips of the individual engraving elements in the axial direction of the printing cylinder due to axial displacement of the engraving elements on the engraving carriage must be set with high precision to the required lane widths according to the traditional method, and the engraving carriage with the exactly spaced engraving elements must then be displaced relative to the printing cylinder such that the engraving stylus tips are positioned to the respective, axial engraving start position of the engraving lanes. It is thereby not so much a matter of the absolute setting of the lane widths within an allowable range of tolerances but that all lane widths on a printing cylinder exactly coincide within the range of tolerance.
The traditional alignment of the engraving stylus tips of the engraving elements to the lane widths to be engraved occurs essentially manually by an operator in that the operator initially roughly sets the spacings of the engraving elements corresponding to the lane widths and then finely positions the engraving stylus tips of the engraving elements with visual observation of the engraving stylus tips with the assistance of a specific microscope unit (stylus allocation gauge) and manually actuatable spindle drives.
This manual procedure is time-consuming, particularly when a great number of engraving lanes are to be positioned and, thus, a great plurality of engraving elements must be positioned. Moreover, the adjustment precision is essentially dependent on the care of the operator.
WO Published Application 95/21332 already discloses an apparatus for automatic, axial positioning of a plurality of engraving elements when engraving printing cylinders with the assistance of motor drives for the individual engraving elements arranged on an engraving carriage and a sensor monitoring for the automatic motion sequences.